1. Field of the Invention
The present invention relates to a pipe joint structure or a method of assembling main parts of the pipe joint structure in which a distribution pipe is joined to a vessel for accumulating fluid, in particular, applicable to a pipe joint structure including a vessel for accumulating high pressure fluid such as a common rail body in a common rail type fuel injection system.
2. Description of Related Art
It is known that a pipe joint structure in which a distribution pipe (such as a distribution pipe for a high pressure pump or a distribution pipe for an injector) is joined to a common rail body J1 for accumulating high pressure fuel, as shown in FIGS. 14 to 16 wherein analogous structures are depicted and labeled with common reference characters. In the pipe joint structure shown in FIGS. 14 to 16, the common rail body J1 is provided with a conical shaped pressure receiving seat J2. A conical portion J4 formed at an axial end of a distribution pipe J3 (refer to FIG. 14 and FIG. 16) or a conical portion J6 formed at an axial end of a distribution pipe extension cylinder J5 (refer to FIG. 15) is pressed against the pressure receiving seat J2 of the common rail body J1. A contact surface between the pressure receiving seat J2 and the conical portion J4 or J6 constitutes a fluid tight sealing surface J7.
A cylindrical screw threaded joint fitting J8 is fixed by welding to the common rail body J1. A distributor pipe screw fastening nut J11, which is assembled in advance to the distribution pipe J3, is screwed on to a threaded surface J10 of the screw threaded joint fitting J8 in a state that the distributor pipe screw fastening nut J11 abuts against a step portion J9 at a back of the conical portion J4. By fastening the distributor pipe screw fastening nut J11 into the threaded surface J10 of the screw threaded joint fitting J8, the conical portion J4 of the distribution pipe J3 (or the conical portion J6 of the distribution pipe extension cylinder J5) is strongly pressed against the pressure receiving seat J2 of the common rail body J1 to form a main body sealing surface J7.
In the structure mentioned above, if a mounting position of the screw threaded joint fitting J8 to the common rail body J1 is shifted, it becomes very difficult to form the main body sealing surface J7 since the conical portion J4 or J6 does not coincide accurately with the pressure receiving seat J2. Accordingly, in the conventional structure, the screw threaded joint fitting J8 has to be mounted on the common rail body J1 with higher dimensional accuracy. To satisfy this requirement, dimensions of parts constituting the common rail body J1 and the screw threaded joint fitting J8 have to be highly accurate and it is necessary to use expensive welding technology such as laser welding technology, which results in higher manufacturing cost.
Further, it is preferable that the common rail body J1 is made of material having higher hardness such as middle or high carbon steel since the common rail body J1 has to endure extremely high pressure. However, though the middle or high carbon steel can be bonded by resistance welding which is not expensive, they can not be bonded by the laser welding whose welding accuracy is high. If low carbon steel is used for the common rail body J1, the laser welding is usable. However, a body size of the common rail body J1 has to be enlarged to ensure high pressure endurance.
Furthermore, in the conventional structure in which distribution pipe J3 or distribution pipe extension cylinder J5 is inserted and positioned inside screw threaded joint fitting J8, the larger size of distributor pipe screw fastening nut J11 is required. This may cause inconvenience for installation to a vehicle. If a smaller size (for example, thread size M12) of distributor pipe screw fastening nut J11 is used for easier installation, thinner wall thickness of screw threaded joint fitting J8 is required, which may cause insufficient strength of screw threaded joint fitting J8.